WO 2005/027978 A2 discloses a number of mono-acylated GLP-1 derivatives including some that are acylated with carboxylic or sulfonic acid.
WO 2011/080103 A1, WO 2012/140117 A1, WO 2012/062803 A1, and WO 2012/062804 A1 disclose a number of double-acylated GLP-1 derivatives including some that are acylated with carboxylic acids.
WO2008/028974 A1 discloses methods for simulating chromatographic separation of mixtures containing a target peptide and related impurities. In Example 1 experiments are carried out with the monoacylated GLP-1 compound liraglutide as the target peptide, in admixture with some impurities believed to be two diacylated, and one tri-acylated variant thereof. These impurities are not further described in the WO publication, as they were not isolated and characterised.